Pediatric depression was almost unthinkable until several years ago. Now we not only know that major depressive disorder (MDD) exists in children and adolescents, but that it is a common condition. It is estimated that children and adolescents who suffer from MDD often develop conduct and anxiety disorders, and that up to 25% develop substance abuse disorder. Consequently, this has resulted in a disproportionate increase in the prevalence of antidepressants prescribed to populations below 20 years of age. Despite the heightened rates in antidepressant use, little is known about the potential long-term behavioral and neural adaptations resulting from antidepressant treatment during early development. To address this problem, the experiments described in this proposal will examine the long-term behavioral consequences of early life (postnatal day [PD] 35-49) exposure to fluoxetine, a selective serotonin reuptake inhibitor, using C57BL/6 male and female mice. This will be accomplished within the framework of the following specific aims: [1] assess long-term consequences of chronic adolescent antidepressant treatment on the sensitivity to reward (drug), mood related behaviors (stress), and memory in adulthood (PD80+), and [2] evaluate the integrity of mood-related biological markers [extracellular signal regulated protein kinase-1/2 (ERK)], within the hippocampal formation, following chronic adolescent antidepressant exposure. It is expected that antidepressant exposure during adolescence will induce long-lived alterations associated with responses to stress, drug-rewarded behaviors, and memory. Furthermore, it is expected that site-specific neurochemical adaptations (ERK fluctuations within the hippocampus) to be a factor mediating these behavioral alterations as a function of juvenile antidepressant exposure. Collectively, the results of this preclinical work will provide first-line evidence on the potential risks of antidepressant exposure during adolescence.